The Nycomed group has developed a carbon centered soluble stable free radical with an extremely narrow EPR spectral line with potential application in Overhauser Imaging and EPR Imaging and Imaging oximetry. Properties of the compound include its EPR oximetric sensitivity, its stability in cellular systems, and its suitability as an EPR oximeter and as an EPR tracer will be investigated. The ultimate sensitivity of this technique will be determined by the stability and uniformity of the magnetic fields.